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In this article we will try to build an automatic battery charger circuit using dump capacitor concept for self detecting and charging a multiple set of batteries. The idea was requested by Mr. Michael.

Requesting a Dump Capacitor Charger Circuit

Hi Swagatam,

My name is Michael and live in Belgium.

I found your site thru google during my search of a battery trickle charger.

I'm still looking for a good circuit, therefore I hope maybe you can help me out.

At home we have a variety of lead acid batteries and during the winter most of them get neglected.

Resulting in spring, a check which battery made it and which one didn't.

Problem is the variety of batteries I'm a biker, my brothers has a small excavator and tractor, we have 2 vans with 2 caravans and we ( I, mother, sister, 2 brothers and there girlfriends) all have a car.

So you see a WIDE variety of batteries, in the past I've bought a smart 7stage charger but it is impossible to take care of all batteries using only one charger.

So I ask if you could design a circuit for me.

With the following specs:

Maintain at least 5 or more batteries simultaneously.

Checks voltage if low dumps a capacitor into the battery.

Able to handle capacities as low as 3 Ah up to 200Ah.

Safe to operate 24/7 with no user input.

Some of the things I've given some thought:

With the use of a cap dump, there's no need for a heavy mains transformer, because the load for transformer is under control.

A selectable capacitor depending on the capacity of the battery.

A problem for me was to find something that could activate multiple outputs on a time base(using a lm311 to sense the voltage, a 555 to dump using mosfet).

An indicator of some sort, which will indicate which battery needed the most dumps or immediate dumps, and locate bad batteries.

If you believe I've made some errors, or my requirements are impossible please let me now.

If you could implement extra features or safety features, I didn't think of do not hesitate to add or modify:)

I'm a student getting a bachelor in Electro Mechanics, I'm a electronic enthusiast, have a room full of components and parts to play with.

But I lack the designer skills for building circuits for my needs.

I hope to have drawn your interest in this problem and hope you find the time to design something for me.

Maybe this circuit could become number hundred on your site!

Also great job with your site and hope al the best for you!

Thanks for sharing all of your effort and time with us!

Sincerely

The Circuit Design

The discussed circuit concept for automatically charging multiple batteries using dump capacitor can be fundamentally divided into 3 stages:

opamp comparator detector stage

IC 555 ON/OFF interval generator

dump capacitor circuit stage

The opamp stages are configured to maintain a continuous sensing of battery charge level, and correspondingly execute the cutoff /restoration of the charging process across the batteries attached with their relevant inputs. The charging process is carried out through capacitor dump system.

Let's undersatnd the various stgaes elaborately:

Self Regulating 4 Battery Opamp Charger Circuit

The first stage within this design is the opamp battery over charge detector circuit, the schematic of this stage can be seen below:

Parts List:

opamps: LM324

presets:10K

zener 6V/0.5 watt

R5 = 10K

diodes = 6A4 or as per the charging specs

We will consider only 4 batteries here, and therefore use 4 opamps for the respective over charge cut offs. A1 to A4 opamps are taken from the quad opamp IC LM324, each configured as compartaors to detect the attached corresponding battery over charge levels.

As can be seen in the diagram the non-inverting inputs of each of the opamps is configured with the relevant battery positives for enabling the required sensing of the battery voltages.

The positives of the individual batteries are connected with the capacitor dump output, which we will discuss in the later part of the article.

The inverting (-) pins of the opamps are designated to a fixed reference level through a single common zener diode.

The presets attached with the (+) or the non-inverting inputs of the opamps and are used for setting up the precise full-charge trip points with respect to the corresponding (-) pin zener reference levels.

The presets are set such that when the relevant battery voltage reaches the full charge level, the proportionate value at the pin(+) of the opamp just goes above the (-) pin zener reference level.

The above situation instantly turns the opamp's output from its initial 0V to a high logic equal to the supply voltage level.

This high at the opamp output triggers an IC 555 atable circuit so that the IC 555 is enabled to produce a periodic ON/OFF intervals over the attached capacitor dump circuit...the following discussion will explain us the proceedings:

IC 555 Astable for Generating periodic ON/OFF

The following schematic shows the IC 555 stage configured as an astable for the intended periodic ON/OFF switching generation for the subsequent capacitor dump circuit.

Parts List

IC = IC 555

R2 = 22K

R1, C2 = calculate to get the desired charge dump cycle rate

As shown in the above diagram, pin#4 which is the reset pinout of the IC 555 is connected with the output of the relevant opamp stage.

Each of the opamps will have its own separate IC 555 stages along with the capacitor dump circuit stage.

While the battery is in the charging process and the opamp output is held at zero, the IC 555 astable stays disabled, however the moment the relevant attached battery gets fully charged, and the concerned opamp output turns positive, the connected the IC 555 astable becomes activated, which causes its output pin#3 to generate a periodic ON/OFF cycles.

The pin#3 of the IC 555 is configured with its own individual capacitor dump circuit, which responds to the ON/OFF cycles from the IC 555 stage and begins the process of charging and dumping a capacitor across the relevant battery.

To understand how this dump capacitor behaves in response to the IC 555 ON/OFF cycles we may have to go through the following section of the article:

Capacitor Dump Charger Circuit:

As per the request the battery is required to be charged through a capacitor dump circuit, and I came up with the following circuit, I hope it would do the job as per the expectations:

The circuit functioning of the above shown capacitor dump charger circuit can be learned following explanation:

As long as IC 555 stays in the disabled state, the BC547 is allowed to get the required biasing through its base 1K resistor, which in turn keeps the associated TIP36 transistor in the ON position.

This situation allows the high value collector capacitor to get charged to its maximum allowable limit. In this position the capacitor is armed in the charged stand-by position.

The moment IC 555 stage gets activated and begins its ON OFF cycle, the OFF periods of the cycle switches OFF BC547/TIP36 pair, and switches ON the extreme left side TIP36, which instantly closes and dumps the charge from the capacitor into the associated battery positive.

The next ON cycle from the IC 555 reverts the situation into the previous conditions and charges the 20,000uF capacitor, and yet again, with the next subsequent OFF cycle the capacitor is allowed to dump its charge via the relevant TIP36 transistor.

This charging and dumping operation is carried out continuously until the corresponding battery becomes fully charged, forcing the opamp to turn OFF itself and the whole proceedings.

All the opamps work in the similar manner, by sensing the attached battery condition and self starting the above explained procedures.

This concludes the explanation regarding the proposed automatic multiple battery charger using capacitor dump charging, if you have any questions or doubts, do not hesitate to communicate through comments...

In this page you will come across more than 100 well researched battery charger circuits which will operate in a technically correct manner and ensure a safe and optimal charging of your battery.

Battery Charging Expertise only in this Site

In other sites you may find many related circuits which are mostly technically incorrect and the authors have no technical expertise to verify it for you or answer to your specific queries.

A battery charger, or recharger, is an equipment accustomed to supply electric power into a supplementary cell or rechargeable battery pack by pressuring an electric current into it.

I have presented more than 100 thoroughly researched best battery charging concepts which promise not only the best possible way of charging your battery but also equipped to implement the same with utmost care and safety.

There are plenty of choices you can get while designing your own battery charger circuit as per your specific needs and battery specs.

For more detailed information regarding the various types of automatic and semi-automatic battery charger circuits, or tutorials please select the one as per your requirement from the list:

Lead acid batteries are the most common type of batteries especially because these can be applied for big and high current applications and these are so far a lot cheaper than Li-ion batteries. Although not as efficient as the Li-ion batts, nevertheless still more popular than other form of batteries. You will discover many good lead acid battery charger circuits in this blog to suit your specific battery specs.

Among all lead acid batteries variants 12V lead acid batteries are the most popular type of batteries and are presently widely used for most of battery driven gadgets. These are ideally suited for applications which require high power output such as in car electrical, inverters, power LED lamps, and with solar charger modules.

Charging a 12V battery requires a good quality charger which must be equipped with a 3 step charging involving High Current Bulk Charging Moderate Current Bulk Charging, Absorption Charging, Float Charging. You can get more details in the above link

6 V Battery Charger Circuits

6V batteries are also mostly found in the form of lead acid batteries, but there application range is relatively limited compared to 12V counterpart. Because being less in voltage means the battery will need to be really huge for delivering high current outputs and therefore are not used in high current applications ranges. Nevertheless the charger circuit for a 6V battery also needs to be equally good with a 3-step charging and auto cut off system. More explanation is provided in the above link

24 V Battery Charger Circuits

Just like 12V batteries 24V batteries are also widely used in a huge number battery operated devices, especially one which involve huge wattage or operate with high current loads. Being higher in voltage ensures lower current even for higher rated loads and helps to keep the system compact. These are also mostly lead acid types preferably with deep discharge facility, and the charging process is quite identical to the above discussed batteries which require a precise auto-cut off system and a long float charging sessions. You will find many related circuit designs in the adjoining link.

48 V Battery Charger Circuits

48V batteries are more robust than the above mentioned batteries and are used only where awesome amount of power is required. It is used in huge solar inverters, GTI or grid tie inverters, and also in inverters which require very long backup operations. To charge a 48V battery you will need to make sure that the output from the charger must be at least 55V rated, and the battery must be charged with a 3 step charging process quite identical to the other lead acid variants.

PWM Battery Charger Circuits

PWM battery charging concept is a relatively modern concept which is used for charging battery through digital circuits and using pulse width modulation. Here the charging process is controlled by varying the voltage pulses to the battery. Since no analogue system is involved PWM chargers are very efficient and dissipate minimum electricity in the form of heat. In this website I have published a good number of PWM based battery charger circuits which anybody can grasp and build at home.

IC 555 Battery Charger Circuits

As we all know that IC 741 is an opamp IC which has been so far used for implementing many useful circuit ideas. In this website you will find that this versatile IC has been smartly applied as a comparator in most battery charger circuits for enabling an automatic full charge cut-off and low discharge restoration implementation. Using a comparator IC allows your battery charging to be entirely safe and ideally suited for charging any battery safely. More can be learned from the attached link.

Just like IC 741, IC 555 is another versatile chip which can be effectively used for making battery charger circuits. I have presented a few battery charger circuits using IC 555 which also features an automatic cut off as soon as the battery is fully charged.

Arduino Battery Charger Circuits

Arduino is a microcontroller concept for designing extremely efficient and state-of-the-art battery charger circuit designs. In this site I have introduced the most modern battery charging technology using Arduino for ensuring the best possible charging implementation for your battery using this highly advanced circuits.

Any electronic hobbyist will know the importance of having a LM317 chip in his electronic goods box, because this IC can do some wonderful jobs when it comes to voltage regulation procedures. A battery charger basically requires a good voltage regulation while charging and this IC makes sure that it gives its best while implementing a safe regulated supply within a battery charger circuit. In this website you will a handful of selected LM317 based battery charger circuits with current control facility.

LM338 is the big brother of LM317 and is identically versatile, and greatly suited for making constant current and constant voltage battery charger circuits, with one added feature. This feature is its high current specifications which makes it even more special than LM317. LM338 van deliver a good 5 amp current therefore becomes suitable for charging batteries upto 50 Ah rating. You will come across many good LM338 based battery charger circuit in this website.

An automatic charger refers to a design which may be equipped with all the necessary features required for a comprehensive and safe battery charging procedure, such as supplying CC/CV to the battery and an auto-cut for both the high and lower thresholds of the battery. A good range of automatic battery charger circuits have been included in this website for your specific battery charging requirement and specs.

In the above discussion we learned how an opamp IC 741 can be used in battery charger circuits for implementing a safe auto cut-off. In this blog you will find many such alternate designs using one opamp and sometimes two opamps for maintaining the required auto cut off action in the most efficient way. Other than IC 741 you will also find see how other variants such as IC LM321, LM358, LM324 etc are used as effectively for implementing automatic battery charger circuits.

Solar power harnessing is becoming more and more popular and highly sought after technology today. When it comes to solar energy harnessing and solar power accumulation, charging battery effcetively becomes an inherent part of the entire system. In this website I have designed many exclusive solar battery charger circuits, and MPPT charging concepts which can be used for charging batteries using solar panel at the most efficient way.

Simple Battery Charger Circuits

Although battery charging concept normally requires complex steps and procedures for ensuring maximum benefit for the battery and the user, simple battery chargers with bare minimum facilities can be also used for charging batteries as safely. However since these are not equipped with advanced circuitry the charging efficiency might be a little compromised wherein the batteries may not charge upto the optimal levels. A few transistorized simple battery chargers have been included in the above link, specially suited for the young school electronic enthusiasts.

Today we all have cellphones with us and also invariably get a cellphone charger with every cellphone. These are high advanced SMPS based compact battery chargers which ensure optimal charging response for the sensitive Li-ion battery inside a cellphone. I have presented a few ideally suited SMPS based cellphone charger circuits for charging cellphone batteries.

We have discussed the term constant current and constant voltage in the above sections. Basically these mean that the current supply and the voltage supply from the specific charger must be controlled and not allowed to exceed the stipulated safe limits of the connected battery. These parameters become crucial mostly for the Li-ion batteries and requires strict implementation with these features. In this website you will be able to find elaborate designs explaining CC/CV based battery chargers for your individual application needs.

Li-ion batteries are special type of batteries which are designed to produce maximum efficiency in the form of quick charging, long backups, along with a huge number charging/discharging cycles. Being so efficient also means that these batteries will require an equally sophisticated charging system. In this website I have furnished a handful of good Li-ion battery charger circuits,which are cheap yet include all the necessary advanced features such as constant current, contact voltage and auto cut-off features with automatic temperature sensing and current sensing trip off facilities.

Universal Battery Charger Circuits

A universal battery charger must have all the features in it which can make it universally applicable for charging all types of batteries, such as lead acid battery, Ni-Cd battery, SMF battery and also Li-ion battery. To meet these crucial criteria a universal charger must have all the settings which can be applied for a given battery charging specifications, and must be user friendly also. In this website I have designed a few good universal and smart battery charger circuits which are truly universal, as its name suggests.

High Current Battery Charger Circuits

A the name suggests a wireless battery charger allows the user to charge a given battery without physically connecting it with the charger though wires, or simply put the battery charger and the battery are connected through electric induction and without any wire connections. If you search for wireless battery charger in this website you will be amazed to learn the easy procedures which will enable to build this wonderful concept or charging batteries without wires.

I have presented more than 100 best assorted, well researched tutorials regarding battery charger designing and concepts, for more info you can go through the following link

CIRCUIT DESCRIPTION

It comes with a SOP package and hardly any external component count making the IC TP4056 specially applicable for portable Li-Ion chaging applications.

In addition, the TP4056 can also work with USB and wall socket based adapter supplies.

The design does not depend on any blocking diode due to the presence of an internal PMOSFET architecture which is configured to prevent any sort of negative Charge Current in the Circuit.

A special Thermal feedback loop is included in order to regulate the charge current to limit the body temperature while using in high power operation mode or with high ambient temperatures.

The full charge voltage is fixed at 4.2V, while the charge current can be adjusted externally through a given single resistor.

The IC TP4056 is featured to automatically shut down the charging cycle as soon as the charge current has dropped to 1/10th the set value, after the final float voltage is accomplished.

Some of the other mains features of this IC TP4056 include a built-in current monitor circuitry, an under voltage lockout, an automatic recharge resumption, and a couple of status pinouts to indicate full-charge cut off and the supply input voltage switch ON.

IC TP4056 image and pinout arrangement

FEATURES and SPECIFICATIONS

·Charge Current may be programmed to a max 1000mA

·The circuit can be free of power devices, Sensing Resistor or a Blocking Diode
·A full fledged Linear Charger in SOP-8 Package for charging applications of Single Cell Lithium-Ion Batteries.

APPLICATIONS

Pinout specification and functioning details of TP4056 IC

TEMP(Pin 1) :Temperature Sense Input

Hooking up TEMP pin with an NTC thermistor's output in Lithium ion battery pack. If TEMP pin’s voltage goes under 45% or over 80% of supply voltage VIN exceeding 0.15S, this indicates that
battery’s temperature is simply too high or overly reduced, charging at this position is stopped. The temperature detection feature could be disabled by joining the TEMP pinto the ground rail.

PROG(Pin 2): is associated with the Constant Charge Current Setting and may be set by attaching a resistor RI(prog) from this pin2 to GND.

While in the precharge mode, the ISET pin’s voltage is regulated to around 0.2V. and in constant charge current mode, the ISET pin’s voltage is regulated to around 2V. Within all modes and in the process of charging, the voltage on ISET pin could be utilized to monitor the charge current through a meter.

GND(Pin3): Ground Terminal

Vcc(Pin 4): Positive Input Supply Voltage

VIN is the power supply input for the internal circuit to operate. Any time VIN falls at around 30mv below the BAT pin voltage, TP4056 goes into low power sleep mode, reducing BAT pin’s current below 2uA.

BAT(Pin5): Battery Connection Pin.

Link the positive terminal of the battery to BAT pin. BAT pin consumes lower than 2uA current whenever the chip is in the disable mode or in sleep mode. BAT pin offers charge current for the connected battery and presents it with a voltage regulation of precise 4.2V.

(Pin6): Open Drain Charge Status Output, Whenever the battery reaches the Charge Termination shut off point, this pinout is dragged low through an in-built switch, but normally this pin remains in high impedance status.

(Pin7): Open Drain Charge Status Output Once the battery is connected and begins charging, this pinout is taken low by an in-built switch, in any other case the pin is held at high impedance condition.

CE(Pin8): Chip Enable Input. A high input here enables the unit to be in the typical operating mode.

Towing the CE pin to a logic low level will force the TP4056 chip into a disable or shut down mode.

The CE pin is compatible and could be associated wit TTL or CMOS logic triggers.

Li-Ion Battery charger circuit using TP4056

The following design represents the typical Li-ion battery charger circuit with constant current and constant voltage features and with auto termination at 4.2V.

The following figure shows the LED status indication details for the above discussed CV, CC Li-Ion battery charger circuit.

In this article we learn regarding how to design and make your own customized high current wireless battery charger circuit using wireless power transfer concept.

Introduction

In many of my earlier articles I have comprehensively discussed wireless power transfer, in this article we will go a step ahead and try to learn how to design a high current version of the same which can be applied for any high power wireless transfer operation such as for charging an electric car battery etc.The idea of optimizing a wireless power transfer circuit is quite similar to optimizing an induction heater circuit, wherein both the concepts can be seen utilizing the optimization of their LC tank stage for achieving the desired power output at the highest possible efficiency.

The design can be implemented by utilizing the following basic circuit stages in it:

The Transmitter Circuit will include:

The Receiver circuit stage will include:

1) Only the LC circuit stage.

An example circuit for the proposed high current wireless battery charger can be witnessed in the following diagram, for simplicity sake I have eliminated the use of a full bridge or half bridge circuit, rather have incorporated an ordinary IC 555 circuit.

The above design represents the transmitter circuit of the high power wireless battery charger circuit using a IC 555 PWM circuit.

Here the output could be a little inefficient since the conduction process is single sided and not a push pull type.

Still, if this circuit is correctly optimized a decent high current power transfer can be expected from it.

How the Circuit Works

The IC 555 is basically configured in its standard PWM mode which can be adjusted using the shown 5K pot, there's another adjustable resistor in the form of 1M pot which can used for optimizing the frequency and the resonance degree of the circuit.

The PWM pot could be used for adjusting the current level while the 1M for peaking the resonance level of the LC tank circuit.

The LC tank circuit can be seen attached with the transistor 2N3055 which powers this LC stage with a frequency corresponding to its base frequency from pin#3 of the IC.

The Receiver Circuit

The receiver circuit for this high current wireless battery charger can be simply made by utilizing the LC stage of the transmitter circuit, meaning you can just replicate the LC stage from the transmitter circuit and keep it in parallel to the transmitter's LC stage for achieving the wireless power transfer.

Make sure the LC values are exactly similar to the Tx LC values. The set up can be seen in the following image:

The 2N2222 transistor is introduced to make sure that while adjusting the resonance, the 2N3055 is never subjected to an over current situation. In case this tends to happen the over current develops an equivalent amount of triggering across Rx sufficient to activate the 2N2222, which in turn shorts the 2N3055 base to ground inhibiting it from conducting any further and thus preventing the device from a possible damage.

Rx may be calculated using the following formula:

Rx = 0.6/Max current Limit of the transistor (or the wireless power transfer)

Adding a voltage regulator for charging the battery:

In the above diagram, the output from the receiver should be attached with a voltage regulator circuit such as using an LM338 circuit or an opamp controller circuit for making sure that the output can be safely fed to the intended battery for charging it.

If you have any further queries, please feel free to express them through your comments.

This universal automatic battery charger circuit is extremely versatile with its functioning and can be adapted for all types of battery charging and even for solar charge controller application.

Universal Battery Charger Main Features

A universal battery charger circuit must have the following main features included in it:1) Automatic battery full charge cut-off, and automatic low battery charging initialization, with corresponding LED indicator warnings.2) Adaptable to all types of battery charging

Out of the above 5 features the first 3 are crucial and become the mandatory features for any universal battery charger circuit.

However along with these features an automatic battery charger must also be extremely compact, cheap, and easy to operate, otherwise the design could be quite useless for folks with less technical knowledge, making the "universal" tag get nullified.

However with an automatic battery charger using hysteresis in opamp adjusting the feedback preset or variable resistor becomes a crucial procedure and a little complicated affair especially for the newcomers..since it requires some relentless trial and error process until the correct setting is finalized.

Additionally setting up of the overcharge cut-off also becomes a tedious process for any newcomer who may be trying to achieve the results quickly with his battery charger circuit.

Using Fixed Resistors instead of Pots or Presets

The present article specifically focuses on the above issue and replaces the pots and presets with fixed resistors in order to eliminate the time consuming adjustments and to ensure a hassle free design for the end user or constructor.

I have already discussed one earlier article which elaborately explained hysteresis in opamps, we are going to use the same concept and formulas for designing the proposed universal battery charger circuit which will hopefully solve all the confusions related to the building of a customized battery charger circuit for any unique battery.

Before we move ahead with an example circuit explanation, it would be important to understand why hysteresis is required for our battery charger circuit?

It's because we are interested to use a single opamp and use it for detecting both the lower discharge threshold of the battery as well as the upper full charge threshold.

Importance of Adding a Hysteresis

Normally, without hysteresis, an opamp cannot be set for triggering at two different thresholds which may be quite wide apart, therefore we employ hysteresis to get the facility of using a single opamp with a dual detection feature.

Coming back to our main topic regarding designing an universal battery charger circuit with hysteresis, let's learn how we can calculate the fixed resistors, so that the complex Hi/Lo cut off setting up procedures using variable resistors or presets can be eliminated.

In the above example illustrations, we can clearly see how the hysteresis resistor Rh is calculated with respect to the other two reference resistors Rx and Ry.

Now let's try to implement the above concept into an actual battery charger circuit and see how the relevant parameters may be calculated for getting the final optimized output. We take the following example of a 6V battery charger circuit

In this solid state charger diagram, as soon as pin#2 voltage becomes higher pin#3 reference voltage, the output pin#6 goes low, switching OFF the TIP122 and the charging of the battery. Conversely as long as pin#2 potential stays below pin#3, the output of the opamp keeps the TIP122 switched ON and the battery continues to charge.

Implementing the Formulas in a Practical Example

From the formulas expressed in the previous section we are able to see a couple of crucial parameters which needs to be considered while implementing it within a practical circuit, as given below:

1) The reference voltage applied to Rx and the opamp supply voltage Vcc must be equal and constant.

2) The selected upper battery full-charge switch off threshold and the lower battery discharge switch ON threshold voltages must be lower than the Vcc and the reference voltages.

This looks a little tricky because the supply voltage Vcc generally is connected with the battery and therefore it cannot be constant, and also it cannot be lower than the reference.

Anyway, to tackle the issue we make sure that the Vcc is clamped with the reference level, and the battery voltage which needs to be sensed is dropped to a 50% lower value using a potential divider network so that it becomes less than the Vcc, as shown in the above diagram.

The resistor Ra and Rb drop the battery voltage to a proportionate 50% lower value, while the 4.7V zener sets the fixed reference voltage for Rx/Ry and the Vcc pin#4 of the opamp. Now things look ready for the calculations.

So let's apply the hysteresis formulas to this 6V charger and see how it works out for this example circuit:

In the referred 6V circuit above we have the following data in hand:

Battery to be charged is 6V

Upper cut off point is 7V

Lower restoration point is 5.5V.

Vcc, and reference voltage is set to 4.7V (using 4.7V zener)

We select Ra, Rb as 100k resistors to reduce the 6V battery potential to 50% less value, therefore the upper cut off point 7V now becomes 3.5V (VH), and the lower 5.5V becomes 2.75V (VL)

Now, we need to find out the values of hysteresis resistor Rh with respect to Rx and Ry.

As per the formula:

Rh/Rx = VL / VH - VL = 2.75 / 3.5 - 2.75 = 3.66---------1)

∴ Rh/Rx = 3.66

Ry/Rx = VL / Vcc - VH = 2.75 / 4.7 - 3.5 = 2.29----------2)

∴ Ry/Rx = 2.29

From 1) we have Rh/Rx = 3.66

Rh = 3.66Rx

Let's take Rx = 100K,

Other values like 10K, 4k7 or anything could do, but 100K being a standard value and high enough to keep the consumption reduced becomes more suitable.

∴ Rh = 3.66 x 100 = 366K

Substituting this value of Rx in 2), we get

Ry/Rx = 2.29

Ry = 2.29Rx = 2.29 x 100 = 229K∴ Ry = 229K

The above results can be also achieved using a hysteresis calculator software, just by clicking a few buttons

That's it, with the above calculations we have successfully determined the accurate fixed values of the various resistors which will make sure that the connected 6V battery automatically disconnects at 7V, and restarts charging the moment its voltage drops below 5.5V.

For higher voltages such as for achieving 12V, 24V, 48V universal battery circuit, the above discussed design may be simply modified as given below, by eliminating the LM317 stage.

The calculation procedures will be exactly the same as expressed in the previous paragraph.

For high current battery charging, the TIP122 and the diode 1N5408 may need to be upgraded with proportionately higher current devices, and change the 4.7V zener to a value that may be higher than 50% of the battery voltage.

The green LED indicates the charging status of the battery while the red LED enables us to know when the battery is fully charged.

This concludes the article, which clearly explains how to make a simple yet universally applicable battery charger circuit using fixed resistors to ensure extreme accuracy and foolproof cut offs across the set threshold points, which in turn ensures perfect and a safe charging for the connected battery.

The post discusses a two opamp low high battery charger controller circuit which is not only accurate with its features but also allows a hassle free and quick setting up of its high/low cut-off threshold limits. The idea was requested by Mr. Mamdouh.

Battery Charger Using 2 Opamps

Hi Mr Swagatam,

I've got the idea, please bear with me, because I'm new to circuits design. i actually thought about using opamps to create the circuit that i need, so that makes me feel better i was heading in the right direction.

However, how can i upgrade this smart emergency light circuit to operate on 26-30 volts and 3 amps. I'll be using a dc to dc voltage booster and steady current between the battery and this circuit, as the battery wont be able to supply the required voltage.

so, I'm not sure if this circuit will still remain to operates with the voltage booster between the battery and the circuit. also, i will have another voltage booster to be connected the main power adapter as the adapter will only produce 19v and i need 26-30 volts. I'm kinda lost with this part because i need circuit to:

1) as soon as i connect the external power automatically it will disconnect the battery and supply the system, in the mean while charging the battery.

2) overcharging protection ( which included in the above design).

3) battery low and full charging indicates (which included in the above design).

4) also i don't know what is the formula to help how to determine the voltage required across my battery to charge it with( battery will be extracted of old laptops.total will be 22V with 6 apms at no load)

5) also, i don,t know the formula to indicate how long my battery will last, and how to calculate the time if i want a battery to last me two hours.

Also, the cpu fan will supplied by the system too. it would be great too to add the option of a dimmer, my original plane was to vary between 26-30 v not need much more than that.

it's a flash light design but using higher wattage LED. I'm sorry for those many questions, but i'm trying to get help and improve my skills in designing as i'm very new to electronics world.

Circuit Schematic

The Circuit Design

In all of my previous battery charger controller circuits I have used a single opamp for executing the full charge auto cut-off, and have employed a hysteresis resistor for enabling the low level charging switch ON for the connected battery.

However calculating this hysteresis resistor correctly for achieving the precise low level restoration becomes slightly difficult and requires some trial and error effort which can be time consuming.

In the above proposed opamp low high battery charger controller circuit two opamp comparator are incorporated instead of one which simplifies the set up procedures and relieves the user from the long procedures.

Referring to the figure we can see two opamps configured as comparators for sensing the battery voltage and for the required cut-off operations.

Assuming the battery is s 12V battery, the lower A2 opamp's 10K preset is set such that its output pin#7 becomes high logic when the battery voltage just crosses the 11V mark (lower discharge threshold), while the upper A1 opamp's preset is adjusted such that its output goes high when the battery voltage touches the higher cut off threshold, say at 14.3V.

Therefore at 11V, the A1 output gets positive but due to the presence of the 1N4148 diode this positive stays ineffective and blocked from moving further to the base of the transistor.

The battery continues to charge, until it reaches 14.3V when the upper opamp activates the relay, and stops the charging supply to the battery.

The situation is instantly latched due to the inclusion of the feedback resistors across pin#1 and pin#3 of A1. The relay becomes locked in this position with the supply completely cut off for the battery.

The battery now begins slowly discharging via the connected load until it reaches its lower discharge threshold level at 11V when the A2 output is forced to go negative or zero. Now the diode at its output becomes forward biased and quickly breaks the latch by grounding the latching feedback signal between the indicated pins of A1.

With this action the relay is instantly deactivated and restored to its initial N/C position and the charging current yet again begins flowing towards the battery.

This opamp low high battery charger circuit can be used as a DC UPS circuit also for ensuring a continuous supply for the load regardless of the mains presence or absence and for getting an uninterrupted supply through out its usage.